The invention relates to a piston or plunger pump comprising at least one piston or plunger; a cylinder part coaxial thereto which accommodates a working chamber of the piston or plunger; a cylinder head which accommodates a cyindrical pressure chamber which is coaxially disposed relative to the piston or plunger and is connected to a pressure line; and a central valve housing which is axially arranged between the working chamber of the piston or plunger and the pressure chamber, which is sealed relative to the cylinder part and also the cylinder head by means of seals and which has seats for suction and discharge valves arranged at its end faces, at least one axial passage controlled by the discharge valve and also a suction passage extending from its peripheral surface to the suction valve side end surface and controlled by the suction valve.
Pumps of this type of construction, which is, for example known from DE-AS No. 17 28 243, fundamentally offer favourable preconditions for the construction of a high pressure pump which makes it possible to generate or to maintain a very high pressure difference, for example 1000 bar. This originates from the fact that the working chamber for the piston or plunger which is subjected to extremely strong pulsations is provided in the form of a cylindrical bore in the cylinder part which is formed as a tubular part without radial openings which penetrate the cylindrical bore and which can therefore be loaded to a particularly high degree, also with respect to pulsating pressures.
The central valve housing is admittedly also subjected to strong pressure pulses when the pumped medium is thrust, during the pressure stroke of the piston or plunger, from the working chamber of the piston or plunger through the axial passage of the central valve housing into the pressure chamber, with the central valve housing being--theoretically--less resistant to pulsations because of its comparatively complicated shape. However, this lower degree of loadability cannot in practice lead to any form of breakdown because the pump valves, and thus also the central valve body which has the valve seats, are parts subject to wear which must in any event be exchanged from time to time.
In the pumps set forth in DE-AS No. 17 28 243 the exchanging of the valves is, however, made exceptionally difficult because the cylinder head, which in DE-AS No. 17 28 243 also accommodates the suction lines of the pump, surrounds the pressure chamber without a joint as a unitary part in such a way that the pressure chamber only needs to be sealed against the outside, or against the suction side of the pump, by a single high pressure seal arranged between the cylinder head and the central valve housing. Thus the advantage of being able to seal the pressure chamber by means of a single seal is bought with the disadvantage that the entire valve head must be dismantled in order to exchange the pump valves.